Stellenbosch University (2011)

Aspects of the thermal ecology of the group-living lizard, Cordylus cataphractus : a spatial and temporal analysis

Truter, Johannes Christoff

Titre : Aspects of the thermal ecology of the group-living lizard, Cordylus cataphractus : a spatial and temporal analysis

Auteur : Truter, Johannes Christoff

Université de soutenance : Stellenbosch University

Grade : Thesis (MSc (Botany and Zoology)) 2011

Résumé partiel Thermal ecology is a central theme in reptilian biology because of the thermodynamic rate dependence of virtually all biological processes in these ectothermic animals. Thermoregulation includes active processes (with associated energetic costs related to altered behaviour and physiology) functioning to maintain body temperatures within a preferred temperature range, so that the majority of physiological functions occurs optimally, despite natural variation in the animal’s thermal habitat. The recent development of quantitative thermal indices now allows researchers to describe the thermal habitat and thermoregulatory functioning of an ectotherm within its environment from a cost-benefit perspective. The use of such quantitative biophysical approaches to reptile thermal ecology studies is however limited in the African context. Cordylus cataphractus is one of the best studied cordylids, and exhibits various characteristics atypical for the family, such as permanent group-living, seasonally lowered surface activity, a low resting metabolic rate and large fat bodies. These characteristics are generally thought to be associated with groupliving in a semi-arid habitat, yet, the possible links to thermal ecology remains unexplored. The objectives of the current study was : firstly, to characterize the preferred temperature range (Tp) of C. cataphractus through the use of ecologically realistic laboratory thermal gradients ; secondly, to explore seasonal and geographical variation in thermal preference, by comparing Tp among individuals captured from a coastal and inland population and during different seasons (autumn and spring) ; thirdly, to describe the thermal habitat of a C. cataphractus population during summer, autumn, winter and spring and to then relate these findings to the seasonal activity patterns reported in literature for the species ; fourthly, to describe the seasonal patterns of thermoregulation (during summer, autumn, winter and spring) in a C. cataphractus population through quantitative thermoregulatory indices ; fifthly, to assess geographic variation in the thermal habitat and IV associated patterns of thermoregulation in C. cataphractus among a coastal population (western range limit) and an inland population (eastern range limit). The thermal habitat of C. cataphractus was described by measuring operative environmental temperatures (Te) with hollow copper lizard models placed around rocks according to the natural surface movement patterns of the species. Variation in thermal habitat quality was subsequently calculated (de = |Te – Tp|) and averaged. Field body temperatures (Tb) of lizards were measured with dorsally attached miniature temperature loggers. Thermoregulatory indices were calculated from Te, Tb and Tp, describing : thermoregulatory accuracy, the effectiveness of thermoregulation and thermal exploitation for each population (coastal and inland) for the respective sampling periods